An automatic refracto-keratometer is a precise measuring-instrument used in the field of ophthalmic optics, in which optical equipments, electronic equipments, precise machines and computer programs are integrated. The auto refracto-keratometer accurately, quickly and objectively measures physical features of an eye such as a refractive power, an astigmatism power, an astigmatism axis and so on, with optical and electronic systems. Thus, the refracto-keratometer is generally used for a prescription of eyeglass or contact lens. FIG. 1 is an optical circuit showing a configuration of a conventional automatic refracto-keratometer. As shown in FIG. 1, the conventional refracto-keratometer includes an infrared optical system 10 for examining an alignment and a corneal curvature of an eye 5 to be examined, a fogging optical system 30 for removing an accommodation power of the eye 5 so that the eye 5 is properly relaxed, and a refractive power measuring optical system 50 for measuring a refractive power of the eye 5. In operation, for examining the alignment and the corneal curvature of the eye 5, an infrared light is emitted from a mire ring light source 12 of the infrared optical system 10. The infrared light is reflected by the eye 5 and then reflected by a dichroic mirror 14. The reflected light passes through a relay lens 16, is reflected by an infrared reflecting mirror (a hot mirror) 17, passes through an image forming lens 18 (a relay lens or a collimating lens), and forms an infrared image of the eye 5 on a 2-dimensional imaging device 20. FIG. 2 is a photograph showing an infrared image of the eye 5 formed on the imaging device 20. With the infrared image, the position of the eye 5 is adjusted to be aligned to a central axis of the refracto-keratometer, and a corneal curvature of the eye 5 is also measured from the size of the infrared ring image. The measured corneal curvature is used for prescription of a contact lens
When the eye 5 is aligned to the central axis of the refracto-keratometer, an interim refractive power of the eye 5 is measured with the refractive power measuring optical system 50. Specifically, an infrared light for measuring the refractive power is emitted from an infrared light source 52, and the infrared measuring light passes through a badal lens 54 for focusing the infrared measuring light on a main surface of the eye 5, is reflected by a reflecting mirror 56 and a polarization beam splitter 58 for polarizing the infrared measuring light, and focused on a retina of the eye 5. A signal light, which is reflected and scattered on the retina of the eye 5, passes through the polarization beam splitter 58, an objective lens 60, an image forming lens 62 and a micro-lens array 64. The objective lens 60 focuses the signal light, the image forming lens 62 collimates or converges the signal light, and the micro-lens array 64 splits the converged signal light into multiple signal lights and also focuses the split signal lights. The split signal lights form images of the signal lights on a 2-dimensional imaging device 66 as shown in FIG. 3. Then, a process and control unit 7 calculates the interim refractive power of the eye 5 from the images of the split signal lights.
After the interim refractive power is calculated, the fogging optical system 30 is operated to relax the eye 5. In detail, a white light is emitted from a white light source 32 and then passes through an image layer 34 to produce an image for fixing the eye's attention and also for relaxing the eye's accommodation power. The image produced at the image layer 34 passes through an adjusting lens 36 for focusing the image according to the refractive power of the eye 5, a reflecting mirror 38, and relay lenses 40, 16, and then the image is reflected by the dichroic mirror 14 and directed to the retina of the eye 5. Thus, the image of the image layer 34 is clearly formed on the retina of the eye 5. After forming the image of the image layer 34 on the retina of the eye 5, the adjusting lens 36 is controlled so that the image of the image layer 34 is not focused on the retina of the eye 5 (that is, the image of the image layer 34 becomes unclear to the eye 5), and thereby the accommodation power of the eye 5 is removed. When the accommodation power of the eye 5 is removed, the above-mentioned refractive power measuring process is repeated to obtain the target and accurate refractive power of the eye 5.
Besides the corneal curvature and the refractive power of the eye 5 obtained with the refracto-keratometer shown in FIG. 1, a fitting state of the eye 5 and a contact lens should be examined for a proper prescription of a contact lens. As shown in FIG. 4, to examine the fitting state, a dye, such as a fluorescent substance, is injected to the eye 5, a contact lens is placed on the eye 5, and a blue light, which is sensitive to the fluorescent substance, is irradiated to the eye 5. Then the fitting state between the eye 5 and the contact lens is observed with a slit beam microscope. Generally, the prescription of a contact lens requires several steps, such as a medical examination by interview with a contact lens user, an examination of a front eye, a corneal curvature measurement, a selection of a base-curve, an evaluation of the fitting state, and so on. The interview is conducted to obtain information which is necessary for the prescription of a contact lens. The examination of a front eye is conducted to check the conditions of an eyelid, an eyelash, a cornea, and so on. The corneal curvature measurement is conducted to obtain the curvature of the center of a cornea with a keratometer, a topographer and so on. The base-curve is determined to select a suitable contact lens for the cornea of the eye. The evaluation of the fitting state is conducted to check whether a contact lens properly fits to the eye. The fitting state can be evaluated by examining a dye pattern, movements and positions of contact lens, and so on with an instrument such as a button lamp, a slit beam microscope and so on. In accordance with such evaluation results, suitable contact lens can be prescribed.
In the dye pattern examination, a dye, such as a fluorescent substance, specifically, fluorescein is injected to an eye, a contact lens is placed on the eye, and the fitting state between the eye and the contact lens is observed with a slit beam microscope. When the fluorescein contacts with tear in the eye, the color of fluorescein changes to green, and the locations of tear, specifically the locations of tear between the cornea and the contact lens can be clearly observed, and the fitting state of the contact lens can be properly evaluated. FIGS. 5a˜5c are photographs showing the fitting states of a contact lens on a model eye. The fitting can be generally classified into a steep state (FIG. 5a), a flat state (FIG. 5b) and an alignment state (FIG. 5c). The steep state indicates that a contact lens having a small curvature is selected. In this case, a periphery of the contact lens contacts to the cornea and the tear gathers in the center part of the eye. Thus, tear is not properly circulated, impurities cannot be properly removed from eye, and oxygen cannot be properly supplied to the eye. The flat state indicates that a contact lens having a large curvature is selected. In this case, a large amount of tear is located around the periphery of the contact lens, and the center part of the contact lens contacts to the cornea. Thus, the contact lens user may feel inconvenience in eyelid movements and a corneal xerosis. Furthermore, the contact lens can be dislocated from its original location by the movement of the eye. The alignment state is an ideal state in which a proper amount of tear is uniformly dispersed between the cornea and the contact lens. The slit beam microscope for observing the fluorescein patterns includes an optical part and a mechanical part, and may further includes an electronic part such as a camera. In the slit beam microscope, the fitting state may be directly observed with an eyepiece lens of the optical part or indirectly observed with the camera or a monitor of the electronic part. The examiner observes the fluorescein patterns and determines and evaluates the fitting state of the contact lens on the basis of his or her experience and knowledge.
In the conventional contact lens fitting, at least two apparatuses for a measurement and an observation are necessary. Especially, the observation apparatus simply displays a magnified image of an eye, but doest not provide any useful information. In addition, since at least two apparatuses are necessary, the arrangement of the apparatus is complicated, and a skilled person is necessary for using the apparatus. Thus, the contact lens prescription process cannot be effectively carried out with the prior apparatus.